1. Field of the Invention
The present invention relates to a process for modification of a polymer. More specifically, it relates to a process for modifying a polymer by reacting a polymer capable of decomposing by carbon radicals present in the molecule thereof with a compound having a nitroxide radical in the molecule thereof and a radical initiator.
2. Description of the Related Art
For example, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-182881, it has been proposed to compound stable free radicals such as TEMPO (i.e., 2,2,6,6-tetramethyl-1-piperidinyloxy radical) into rubber to thereby improve the physical properties of the rubber composition, in particular the processability, the abrasion resistance, etc. Further, Japanese Unexamined Patent Publication (Kokai) No. 8-239510 discloses to incorporate a TEMPO derivative into a polymer to thereby prevent polymer aging. However, these are not technologies for positively causing the generation of carbon radicals in a polymer such as rubber and using a compound having the stable free radicals in the molecule thereof to modify the polymer. A technique for using nitroxide radicals to modify a polymer is described in U.S. Pat. No. 4,581,429, but this introduces nitroxide radicals as counter radicals for living radical polymerization and is not used for the purpose of imparting functional groups to the polymer. Japanese National Patent Publication (Tokuhyo) No. 2003-524037 discloses a reaction with multifunctional nitroxide radicals as reversible cross-linking agents in the presence of free radicals, but this is not used for the purpose of imparting functional groups. Therefore, any technology relating to a method for introducing functional groups into a radical degradation type polymer, while suppressing the decrease in the molecular weight has not yet been found.
Ordinary butyl rubber has an extremely low unsaturated degree, and therefore, is superior in weather resistance, heat resistance, ozone resistance, etc., but conversely has the defect of slow vulcanization. In particular, for sufficient vulcanization with sulfur, use of a high temperature and strong vulcanization accelerator, or vulcanization over a long time, is necessary. Therefore, a halogenated butyl rubber improved in vulcanization activity of unsaturated sites by introducing of chlorine or bromine to allyl positions of the unsaturated sites (i.e., isoprene sites) of butyl rubber has been developed. This enables the co-cross-linkability and bondability with other diene-based rubber to be improved, while maintaining the excellent properties of butyl rubber and is, therefore, being widely used. However, in recent years, various measures have been taken to eliminate use of halogens in development of rubber and elastomers from the environmental viewpoints. If considered from the halogen-free viewpoint, the load of halogenated butyl rubber on the environment is large. Further, since halogenated butyl rubber usually is produced by dissolving butyl rubber in a hydrocarbon solvent, followed by halogenation, the number of production steps is large and the production cost is higher than the ordinary butyl rubber.
Technology for grafting maleic anhydride, etc. to a polypropylene in the presence of an organic peroxide (i.e., PO) is generally used. Japanese Unexamined Patent Publication (Kokai) No. 5-59253 discloses a graft of an epoxy group-containing monomer to a polypropylene. However, according to these methods, a decrease in a molecular weight and gelling of a polypropylene-based polymer occur during the modification. Further, production of a homopolymer by a direct reaction of a functional monomer and initiator is unavoidable.